Dear WW: The instructions tell you that the food will keep better if oxygen in excluded. The solid CO2 evaporates, and the CO2 gas pushes air containing oxygen out, and refrigerates food. It warns you not to have solid C02 in contact with food, which could cause "freezer burn". If there were a lot of moisture in the air, it might condense on the solid CO2, and much later when solid CO2 is gone make a puddle that might contaminate the food.
Seems a lot of work and expense ;for a mere bucket of food.
